1. Technical Field
The present invention relates to a shaft coupling through which two shafts are coupled together so that power is transmitted therebetween.
2. Background Art
Shaft couplings are widely different in structure from each other depending on the positional relationship between driving and driven shafts which are coupled together through each shaft coupling so that power is transmitted from the driving shaft to the driven shaft. Typically, such two shafts are positioned so as to be aligned with each other, cross each other, or be parallel to (and not aligned with) each other.
Among shaft couplings through which two parallel shafts are coupled together, Oldham couplings are well-known. Oldham couplings have, however, a problem in that if large power is transmitted between the two shafts, friction surfaces of sliders disposed between the two shafts cannot always be lubricated sufficiently, thus impairing smooth transmission of power. Also, this arrangement does not permit a large offset (diametrical distance between the axes) of the two shafts.
It is also known to couple two parallel shafts together through two constant-velocity joint instead of an Oldham coupling. But in this arrangement, since the working angles of the constant-velocity joints are restricted, in order to increase the offset of the shafts, the axial lengths of the joints have to be increased. This increases the size of the entire apparatus.
JP Patent Publication 2003-260902A discloses a mechanism through which power can be transmitted between two shafts. This mechanism comprises two axially opposed rotary members (disks) and a plate disposed between the rotary members. A plurality of direct-acting guides are provided on each of the front and back sides of the plate so as to extend perpendicular to the corresponding direct-acting guides on the other of the front and back sides of the plate so that power can be transmitted between the rotary members through the plate and the direct-acting guides. This mechanism is short in axial length and thus the entire apparatus is small in size. By arranging steel balls between opposed surfaces in the direct-acting guides that move relative to each other, large power can be smoothly transmitted.
But in this type of shaft coupling, a large number of direct-acting guides are necessary, so that the manufacturing cost of the entire coupling tends to be high. Each direct-acting guide comprises a guide member and a rail member that are movable relative to each other. It is necessary to couple one of the guide member and the rail member to the corresponding rotary member and the other to the plate with high positional accuracy. It is therefore troublesome and time-consuming to mount the direct-acting guides with high accuracy such that their guide member and rail member are smoothly movable relative to each other.